Device and method for developing latent electrostatic images

Abstract

A device for use in developing a latent electrostatic image formed on the image bearing surface of an electrophotographic belt as the belt is moving through an arcuate path includes a container having a quantity of liquid toner. The container includes a top wall that has a centrally located slot and that is shaped to conform to the shape of the top wall. A development electrode is located on the top surface of the top wall. A feed roller is rotatably mounted in the container and positioned so as to project out slightly from the slot in the top wall. In use, the container is positioned with the top wall close to and parallel to the arcuate path of travel of the belt and the feed roller close to but not touching the belt. As the feed roller rotates, liquid toner is brought up close to the belt at which location the toner particles dispersed in the liquid toner are electrically attracted to and deposit on the charged portions of the belt.

What is claimed is: 
     
       1. A device for use in developing a latent electrostatic image formed on the image bearing surface of an electrophotographic belt with liquid toner as said surface is moving through an arcuate path comprising: a. a generally enclosed container for holding a quantity of liquid toner, said container having a top wall including a concave arcuate shaped recessed top wall portion whose curvature conforms to the configuration of curvature of said arcuate path in which the image bearing surface is moving, said concave arcuate shaped recessed top wall portion being concentric with said arcuate path and closely spaced therefrom to define a uniform toning gap therebetween, said top wall recessed portion having an elongate slot therein;   b. a feed roller rotatably mounted within said container, and arranged relative to said arcuate top wall recessed portion, said elongate slot and the arcuate path traversed by said surface whereby the center axes of each are aligned in a vertical plane taken through the center of said slot, said feed roller being sized and positioned so as to contact the liquid toner in the container and a portion of its circumferential surface extending into said slot to direct liquid toner from within the container to said toning gap yet said roller being spaced from said arcuate path of said surface as the belt moves through said gap.   
     
     
       2. The device of claim 1 wherein the container includes at least a transparent front wall portion to permit viewing the liquid toner level within the container. 
     
     
       3. The device of claim 1 wherein the top wall of the container includes an opening to provide a means for filling the container with liquid toner and removable cap means closing off said opening. 
     
     
       4. The device of claim 1 wherein at least a portion of the arcuate shaped top wall portion is electrically conductive, said electrically conductive portion forming the top surface of said arcuate top wall portion and bordering the longitudinal edges of said slot. 
     
     
       5. The device of claim 1 and vent means formed in the top wall of said container along said slot but spaced from said arcuate wall portion and capable of enabling excess liquid toner from said toning gap to reenter said container. 
     
     
       6. A device for use in developing a latent electrostatic image formed on the image bearing surface of an electrophotographic belt with liquid toner as said image bearing surface is moving through a predetermined arcuate path comprising: a. a generally enclosed container capable of holding a quantity of liquid toner, said container having a top wall having a concave arcuate shaped recessed portion at least a portion of which is electrically conductive, the curvature of said recessed portion conforming to the curvature of the arcuate path, said container being positioned such that said top wall portion of the container is concentric with, close to and uniformly spaced from the arcuate path to define a uniform toning gap between said top wall portion and said arcuate path, said top wall portion having an elongate slot;   b. a feed roller rotatably mounted within said container and capable of at least partial immersion within the liquid toner, said feed roller extending out into said slot for directing liquid toner into said uniform gap, the distance between said feed roller and said arcuate path being selected to allow passage of the image bearing surface through said gap without touching said roller or said top wall while said feed roller and the axis of said arcuate path are aligned along a vertical plane taken through the center of said slot.   
     
     
       7. In an electrophotographic copying apparatus of the type including an electrophotographic belt mounted for rotational movement on a plurality of support rollers, a developing device for developing a latent electrostatic image formed on the outer surface of the belt as the surface containing the image is passing over one of the support rollers, the developing device comprising: a. a container positioned adjacent to but spaced from the circumference of said support roller and capable of holding a quantity of liquid toner, the container having a top wall including a recessed portion;   b. an arcuate shaped development electrode as a part of the recessed portion of said top wall, the curvature thereof conforming to the curvature of said support roller and defining a uniform gap between the upper surface thereof and the belt as the belt travels in an arcuate path over said support roller;   c. an elongate through slot formed in said electrode and top wall; and   d. a feed roller rotatably mounted in the container and positioned to communicate with said slot so as to transport liquid toner thereon from the interior of the container to the development electrode surface to fill said gap in the vicinity of the belt at the support roller, said support roller and said feed roller arranged with their longitudinal axes aligned in a vertical plane taken through the center of said slot.   
     
     
       8. The device of claim 7 wherein opposite edges of said top wall bordering said slot are arcuately beveled to present an arcuate surface facing the circumferential surface of said feed roller and concentric therewith. 
     
     
       9. A method of developing a latent electrostatic image formed on the image bearing surface of an electrophotographic belt with liquid toner as said surface is moved through an arcuate path comprising: a. positioning a development electrode having an arcuate surface whose curvature conforms to the curvature of the arcuate path such that the arcuate surface is concentric with, close to but uniformly spaced from said arcuate path, the space between the arcuate surface of the development electrode and the arcuate path defining thereby a toning gap therebetween;   b. transporting liquid toner from a supply to said toning gap by means of a feed roller as the belt is passing through the gap;   c. immersing the feed roller within the liquid toner, spacing the feed roller sufficiently close to said development electrode to enable feed of said liquid toner to said gap in the absence of engagement of said feed roller with said arcuate surface of said image bearing surface; and   d. said method including the additional step of applying clear insulating liquid to the image bearing surface of the electrophotographic belt just prior to entry thereof into said toning gap whereby to prewet said surface, said insulating liquid being the same as that carrying the toner particles of said liquid toner.